Mercury arc rectifier system



Nov. 5, 1929. J. c. READ 7 1,734,915

MERCURY ARC RECTIFIER SYSTEM Filed Aug. 28. 1928 D. C. VOLTS 0 I 0.0.AMPS.

Inventor:

7 John C.Read, by His Attorney.

Patented lqov 5," 1929 I i 101m 0. mp, or RUGBY,

ENGLAND, ASSIGNOB 'ro GENERAL ELEc'rmc comm, A

conrona'rron or NEW'YORK nnncunr no nncrrrmn sys'rnm Application filedAugust 28, 1928,8eria1 No. 802,571, and in Great Britain September 15,1987.

in which this star is divided into a number of. similar symmetricalstar-connected systems.

or groups whosejndividual neutral points are connectedtogether throughone or more interphase transformers to form the main neutral point whichis the negative pole of the D. C. system supplied by the rectifier.

Many types of such interphase transformers are known but all of themhave the common feature that they produce a rapidrise of the rectifiedvoltage from light load to noload. due to the fact that at very smallloads the current flowing through the interphase 2 transformer is notsuflicient to produce the required voltage across it. This rise ofvoltage at no-load is sometimes objectionable, and various meanshave'been taken to prevent it, such as employing less advantageoustransformer connections in which the interphase transformer is not used,or connecting a load resistance by hand or automatically across therectifier when the usefulload on the latter drops low, so that the totalcurrent output of the rectifier never'falls below the critical value atwhich its voltage would start to rise sharply. The first of thesemethods involves a more costly transformer and other disa.d,

waste of power. The object of the present invention'is'to prevent thisrise of voltage in a wa which does not involve these objections anactually saves power.

, The novel features which I consider characteristic of my invention arepoi'ntedflout in the appended claims. The invention itself however, willbest be understood by reference to the accom anying drawing in whichFig. 1 illustrates in ammatically a system of connections accor ing tothe invention, as

vantages; the second entails a considerable applied to one typical formof interphase '11, and whose free ends are respectively connected to'theanodes of rectifier B. This is a well-known system of connections forlarge electric arc rectifiers. Switches 12, 13 and 14,

which are all operated together, are capable of switching in anincreased number of turns inthe phases of the primary winding. An

additional switch 15 is operated with 12, 13 7 and 14, so that when thelatter switch in the extra turns in the primary .phases switch 15 w1llsimultaneously short-circuit the interphase transformer.

In Fig 16 is the type of volt-ampere characteristic normally obtainedwith transformer connections as in Fig. 1,- having-a sharp rise of D. C.voltage from the point 17 to no load. The operation of the switches in Fig." 1 is however as follows: at some small load indicated by the point-18, slightly in excess of the critical load at the point 17 where theknee of the curve 16 occurs, the switches12, 13, 14 and 15 are changedover by hand or automatically from the right hand position to the lefthand os'ition in Fig. 1.

Theefiect of short-circuitmg the interphase transformer "wouldbe toincrease the D. C. voltage from the point 18 to the point 19. thevolt-ampere characteristic bein then that given by the line 20; theproof 0% this fact is well-known. But the simultaneous changing over ofswitches 12, 13 and 14 alters the transformer ratio and thereby theactual change of voltage is not from 18 to 19 but from 18 to 21; theactual amount of change from 18 to 21 can of course be adjusted by thechoice of the number of extra turns switched in by the changing over ofswitches 12, 13 and 14. The D. C. volt-ampere characteristic isconsequently given by curve 16 down to the load at which the switchesare thrown over, and from that point to no load by the curve 22.Consequently this arrangement enables a nearly constant voltage to beobtained even down to no load.

The extra turns which are switched in on the transformer primarywindings are seen to be only in circuit at light loads and consequentlyare inexpensive since they have not to be designed to carry any largecurrent. Also, the switchin in or the additional turns reduces thefluxensity in the transformer core, and thereby reduces the standby lossesof the equipment considerably during the periods of light load.

Switches 12, 13 and 14 must be so arranged that they are capable ofchanging from the one position to the other without interrupting theprimary current and without dead-shortcircuiting any part of the rimarywinding.

Many ways of eifecting this are known, and

this feature has therefore been omitted from Fi 1 for simplicity.

Exactly similar arrangements may be used with any other type ofinterphase transformer or interphase transformers, the feature beingthat in all cases the various star points which are normally held apartby the interphase transformer are short-circuited together by switchesand the number of effective turns in the primary phases simultaneouslyincreased.

' What I claim as new and desire to secure by Letters Patent of theUnited States, is

1. The method of preventin a rise of the direct current voltage atno-loa I in a mercury arc rectifier system including a power transwithsecondary windings arranged in groups and connected to the anodes ofsaid rectifier, an interphase transformer connected between said groups,and means for short-circuitmg said interphase transformer andsimultaneouslydecreasing the voltage induced in said secondary winding.

5. In a rectifying stem the combination of a mercuryarc recti er, apower transformer provided with secondary windings arranged in groupsand connected to theanodes of said rectifier, an interphase transformerconnected between said groups, and means for short-circuitin said interhase transformer. and simufianeously c anging the ratio of said wertransformer.

6. In a rectifying s stem the combination of 'a mercury arc recti er, apower transformer provided with secondary windings arranged in groupsand connected to the anodes of said rectifier, an interphase transformerconnected between said groups, and means for short-circuiting saidinterphase transformer and simultaneously increasing the number of Iturns in the primary winding of said power transformer.

In witness whereof, I have hereunto set my hand this 27th day of August,1928.

' JOHN C. READ.

former provided with secondary windings separated into groups andconnected to the anodes of the rectifier and an interphase transformerconnected between said groups, which consists in short-circuiting theinterphase transformer at a predetermined load and simultaneouslydecreasing the voltage impressed upon said anodes.

2. The method of preventin a rise of the direct current voltage at noloa in a mercury are rectifier system including a power transformerprovided with secondary windings separated into grou s and connected tothe anodes of the rectifier and an interphase transformer connectedbetween said groups, which consists in short-circuiting the interphasetransformer at a predetermined load and simultaneously changing theratio of said ower transformer.

3. The method of preventing a rise of the direct current voltage atno-load in a mercury arc rectifier system including a power transformerprovided with secondary windings separated into groups and connected tothe anodes of the rectifier and an interphase transformer connectedbetween said groups, which consists in short-circuiting the interphasetransformer at a predetermined load

